Thermoplastic polymer composition and method for making articles and films from the same

ABSTRACT

A thermoplastic polymer composition comprises a polyethylene polymer composition and a salt of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid. The polyethylene polymer composition can have a Melt Relaxation Product of 50,000 or less. A method for producing an injection molded article comprises the steps of (a) providing a thermoplastic polymer composition as described above, (b) melting the thermoplastic polymer composition, (c) injecting the molten thermoplastic polymer composition into a mold cavity, (d) cooling the molten thermoplastic polymer composition, and (e) ejecting the injection molded article from the mold cavity. A method for producing a film comprises the steps of (a) providing a thermoplastic polymer composition as described above, (b) melting the thermoplastic polymer composition, (c) extruding the molten thermoplastic polymer composition through a slot-shaped die orifice to form a film, (d) cooling the film, and (e) collecting the film.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims, pursuant to 35 U.S.C. § 119(e), priority to andthe benefit of the filing date of U.S. patent application Ser. No.63/141,546, which was filed on Jan. 26, 2021, the contents of which arehereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The invention relates to thermoplastic polymer compositions and methodsfor making articles (e.g., injection molded articles) and films (e.g.,cast films) from the same.

BACKGROUND

Several nucleating agents for thermoplastic polymers are known in theart. These nucleating agents generally function by forming nuclei orproviding sites for the formation and/or growth of crystals in thethermoplastic polymer as it solidifies from a molten state. The nucleior sites provided by the nucleating agent allow the crystals to formwithin the cooling polymer at a higher temperature and/or at a morerapid rate than the crystals will form in the virgin, non-nucleatedthermoplastic polymer. These effects can then permit processing of anucleated thermoplastic polymer composition at cycle times that areshorter than the virgin, non-nucleated thermoplastic polymer. Nucleatingagents can also produce an orientation of crystalline lamellae in thepolymer that would not result in a polymer that undergoes self-nucleatedcrystallization. Depending on the orientation of crystalline lamellaeproduced by the nucleating agent, the physical properties of articlesmade from the polymer can be improved relative to a polymer thatundergoes self-nucleated crystallization.

Further, the effectiveness of a nucleating agent may depend on certainphysical properties of the polymer that is being nucleated. In otherwords, a given nucleating agent may more effectively nucleate apolyethylene polymer having one set of physical properties than anotherpolyethylene polymer having a different set of physical properties. Theeffectiveness of the nucleating agent often depends on several physicalproperties of the polymer. The interrelationship between the variousphysical properties and their effect on the nucleating agent has made itdifficult to readily identify a pairing of nucleating agent and polymerthat will yield a polymer composition having the desiredcharacteristics.

Thus, a need remains for combinations of polymer and nucleating agentthat exhibit favorable nucleation and yield polymer compositions havingdesirable physical properties, such as lower water vapor and oxygentransmission rates. A need also remains for processes utilizing suchbeneficial combinations of polymer and nucleating agent, such asinjection molding and cast film processes. The polymer compositions andmethods described in the application seek to fulfill these needs.

BRIEF SUMMARY OF THE INVENTION

In a first embodiment, the invention provides a thermoplastic polymercomposition comprising:

(a) a polyethylene polymer composition having a Melt Relaxation Productof 50,000 or less; and

(b) a salt of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid.

In a second embodiment, the invention provides a method for producing aninjection molded article from a thermoplastic polymer composition. Themethod comprises the steps of:

-   -   (a) providing a thermoplastic polymer composition comprising (i)        a polyethylene polymer composition having a Melt Relaxation        Product of 50,000 or less; and (ii) a salt of        bicyclo[2.2.1]heptane-2,3-dicarboxylic acid;    -   (b) heating the thermoplastic polymer composition to a        temperature sufficient to melt the thermoplastic polymer        composition so that it may be injected into a mold, the mold        having a mold cavity defining the dimensions of an article;    -   (c) injecting the molten thermoplastic polymer composition into        the mold cavity;    -   (d) allowing the molten thermoplastic polymer composition in the        mold cavity to cool and solidify thereby forming an injection        molded article; and    -   (e) opening the mold and ejecting the article from the mold        cavity.

In a third embodiment, the invention provides a method for producing afilm from a thermoplastic polymer composition. The method comprises thesteps of:

-   -   (a) providing a thermoplastic polymer composition comprising (i)        a polyethylene polymer composition having a Melt Relaxation        Produce of 50,000 or less; and (ii) a salt of        bicyclo[2.2.1]heptane-2,3-dicarboxylic acid;    -   (b) heating the thermoplastic polymer composition to a        temperature sufficient to melt the thermoplastic polymer        composition so that it may be extruded through a die;    -   (c) extruding the molten thermoplastic polymer composition        through a die having a slot-shaped die orifice to form a film        exiting the die orifice;    -   (d) passing the film exiting the die orifice over a cooled        surface to solidify the thermoplastic polymer composition; and    -   (e) collecting the film.

DETAILED DESCRIPTION OF THE INVENTION

In a first embodiment, the invention provides a thermoplastic polymercomposition comprising a polyethylene polymer composition and a salt ofbicyclo[2.2.1]heptane-2,3-dicarboxylic acid.

The polyethylene polymer composition utilized in the composition cancomprise any suitable polyethylene polymer or mixture of polyethylenepolymers. However, it is believed that thebicyclo[2.2.1]heptane-2,3-dicarboxylic acid salt is more effective atnucleating polyethylene polymer compositions which exhibit greaterdegrees of melt relaxation. During certain melt processing of a polymer(e.g., injection molding or cast film manufacturing), the polymer meltis subjected to extensional thinning or strain as it is extruded througha die. The strain applied to the polymer melt results in a flowdirection orientation of extended polymer chains in the polymer melt. Asthe processed polymer melt cools, these directionally oriented, extendedpolymer chains can return to a less ordered state before crystallizationof the polymer melt. This process is referred to herein as “meltrelaxation.” Alternatively, the directionally oriented, extended polymerchains can remain oriented in the melt and crystallize to form fibrils.These fibrils provide sites which can initiate self-nucleation of thepolymer. If enough of such fibrils form in the polymer as it solidifiesfrom the melt, the resulting strain-induced self-nucleation can becomethe dominant mode of nucleation in the polymer. While self-nucleation ofthe polymer may sound beneficial, the polymer structure produced by suchself-nucleation is generally less favorable for certain desired physicalproperties. For example, self-nucleated polyethylene generally exhibitshigher water vapor and oxygen transmission rates than polyethylene thathas been heterogeneously nucleated with abicyclo[2.2.1]heptane-2,3-dicarboxylic acid salt. Thus, in order tomaximize the degree of nucleation induced by thebicyclo[2.2.1]heptane-2,3-dicarboxylic acid salt, the thermoplasticpolymer composition preferably contains a polyethylene polymercomposition that exhibits sufficient melt relaxation to ensure thatstrain-induced, self-nucleation will not dominate.

The degree of melt relaxation exhibited by a polymer cannot easily bedirectly quantified. Further, it is believed that melt relaxation can beinfluenced by a number of factors, such as molecular weight, breadth ofthe molecular weight distribution, the relative amount of the highmolecular weight fraction in the molecular weight distribution, andbranching or non-linear chains in the polymer. The number of factorsinvolved and the complex relationship between those factors make itdifficult to identify ranges of values for each that will be sufficientto define a polyethylene polymer that exhibits sufficient meltrelaxation. In other words, one might try to define a molecular weightdistribution for polymers that exhibit sufficient melt relaxation, butthe appropriate range will change with the “shape” of the distribution(i.e., the relative amount of the high molecular weight fraction). Thus,while these factors can be considered when attempting to identify apolyethylene polymer that exhibits sufficient melt relaxation, a moredirect and accurate gauge of melt relaxation is needed.

Applicants have found that the complex viscosity (η*) of a polyethylenepolymer melt can, at least in part, lead to a more accurate gauge ofmelt relaxation. The complex viscosity (η*) relies on complex numbersand is composed of a real part referred to as the dynamic viscosity (η′)and an imaginary part referred to as the out-of-phase viscosity (η″).These values are typically obtained by parallel plate rheologyexperiments, which are well known in the industry and described morefully below. The complex viscosity results obtained by such measurementscan be plotted with out-of-phase viscosity as the y-axis and dynamicviscosity as the x-axis. Such a plot is commonly referred to as aCole-Cole plot. For the substantially linear polyethylene polymercompositions that are of interest here, the Cole-Cole plot bends into acircular arc, and this circular arc approximates the circumference of acircle whose cartesian coordinates follow the equation:r ²=(x−h)²+(y−k)².

In the equation above, x corresponds to the dynamic viscosity (η′)value, and y corresponds to the out-of-phase viscosity (η″) value ateach strain rate. The constants h and k represent the offset of thecenter of the circle from the cartesian origin of the Cole-Cole plot inthe x and y direction, respectively. Due to the nature of the complexviscosity, the value of h is a positive number, and the value of k is anegative number. The radius of this circle (i.e., the circleapproximated by the Cole-Cole plot) has been found to be related to thedegree of melt relaxation in a polyethylene polymer composition, withsmaller radii generally being indicative of greater melt relaxation inthe polymer and larger radii generally being indicative of less meltrelaxation in the polymer.

Unfortunately, the radius of the circle to which the Cole-Cole plotgenerally fits cannot reliably be calculated from a single point on theCole-Cole plot. The natural, small variations in the complex viscositymeasurements will yield slightly different radius values for each x,ypair. Therefore, to determine the radius of this circle, it is necessaryto fit the measured dynamic viscosity (η′) and out-of-phase viscosity(η″) values to the foregoing equation using a least squares approach. Inthis fitting process, the radius for each x,y pair is calculated byrearranging the circle equation, and the square of the error (SE) foreach x,y pair is calculated by squaring the difference between theaverage radius (i.e., the radius obtained by averaging the radiuscalculated for each x,y pair) and the radius calculated for thatparticular x.y pair. The sum of the squared errors (SSE) is thencalculated by taking the sum of the SE for all x,y pairs in theCole-Cole plot. The fitting of the data is executed by varying thevalues for h and k until the sum of the squared errors (SSE) isminimized. Since the calculated radius at any x,y pair depends on h andk, the individual radii are updated as a result of fitting h and k, andthe average radius is also simultaneously updated. The resulting averageradius value (i.e., the arithmetic mean of the radii for each x,y pairafter the least squares fit has been performed) will be hereafterreferred to as the average radius of the Cole-Cole plot (r_(avg)).

As stated above, the average radius of the Cole-Cole plot has been foundto be related to the degree of melt relaxation in a polyethylene polymercomposition. However, the average radius of the Cole-Cole plot is alsoaffected by the Melt Flow Index (MFI) of the polyethylene polymercomposition. In particular, for polymers with similar molecular weightdistribution and branching levels, the average radius of the Cole-Coleplot tends to decrease significantly as the MFI of the polyethylenepolymer composition increases and molecular weight decreases. In thiscase, viscosity in general decreases, and it is well known that lessviscous polymer melts, on average, relax more rapidly. But factorsmentioned earlier such as broader molecular weight distribution, highmolecular weight tail, or branching may cause an unexpectedly highradius for a given MFI, resulting in unexpectedly high viscosity andunexpectedly long average melt relaxation times. In addition, the MFIrange typically seen in polymers used for injection molding and castfilm manufacturing can be quite wide. Thus, a need exists to predictwhether resins over a wider MFI range will relax sufficiently in themelt to allow efficient nucleation via heterogeneous nucleation with thebicyclo[2.2.1]heptane-2,3-dicarboxylic acid salt, or whetherinsufficient melt relaxation causes self-nucleation to become importantor even dominate. Therefore, in order to arrive at a measure that is auseful tool in quantifying melt relaxation across a range of polymers,it is necessary to correct or account for the effect of MFI on theaverage radius of the Cole-Cole plot. Given the generally inverserelationship between the two, the inventors have found that this effectcan best be corrected or accounted for by calculating the product of theMelt Flow Index (MFI) of the polymer and the average radius of theCole-Cole plot (r_(avg)) of the polymer. The resulting product ishereafter referred to as the “Melt Relaxation Product” (MRP). Throughextensive experimentation, the inventors have found that the MeltRelaxation Product (MRP) is a good measure of the degree of meltrelaxation in a polymer, with higher MRP indicating lesser degrees ofmelt relaxation and lower MRP indicating higher degrees of meltrelaxation. In simple terms, a higher MFI polymer would normally have alower r_(avg), offsetting the higher MFI in the MRP equation andleveling the magnitude of MRP. But if r_(avg) is unexpectedly high forsuch a high MFI resin, the offset does not occur and MRP increasesconsiderably. This condition is typified by less effective meltrelaxation.

As noted above, the Melt Relaxation Product (MRP) is defined as theproduct of (i) the Melt Flow Index (MFI) of the polyethylene polymercomposition and (ii) the average radius of the Cole-Cole plot (r_(avg))of the dynamic viscosity (η′) and out-of-phase viscosity (η″) of thepolyethylene polymer composition:MRP=MFI×r _(avg).

The Melt Flow Index of the polyethylene polymer composition, which canbe reported in units of decigrams per minute (dg/min) or grams per 10minutes (g/10 min), is measured in accordance with ASTM Standard D1238at 190° C. using a 2.16 kg load. The polyethylene polymer compositionutilized in the embodiments of the invention preferably has an MRP of50,000 or less. More preferably, the polyethylene polymer compositionhas an MRP of about 45,000 or less, about 40,000 or less, or about35,000 or less. The inventors have not identified a lower limit on theMRP for polyethylene polymer compositions suitable for use in thedisclosed polymer compositions. However, given the manner in which it iscalculated, the MRP will be a positive number greater than 1 and can bequite low for many very high MFI polyethylene polymers. Preferably, theMRP is about 100 or more, about 1,000 or more, about 5,000 or more, orabout 10,000 or more. Thus, in a series of preferred embodiments, thepolyethylene polymer composition has an MRP of about 1 to 50,000 (e.g.,about 1 to about 45,000, about 1 to about 40,000, or about 1 to about35,000), about 100 to 50,000 (e.g., about 100 to about 45,000, about 100to about 40,000, or about 100 to about 35,000), about 1,000 to 50,000(e.g., about 1,000 to about 45,000, about 1,000 to about 40,000, orabout 1,000 to about 35,000), or about 10,000 to 50,000 (e.g., about10,000 to about 45,000, about 10,000 to about 40,000, or about 10,000 toabout 35,000).

The Melt Relaxation Product can be determined by any suitable technique.Preferably, the out-of-phase viscosity (η″) and the dynamic viscosity(η′) are measured by parallel plate rheometry at a temperature of 140°C. using a rotational rheometer equipped with 25 mm parallel plates setat a 1.1 mm gap. The polymer sample used for measurement is provided inthe form of a compression molded disc. During the measurement, theangular distance or strain preferably is kept low to remain in thenon-hysteresis region, with a nominal strain of approximately onepercent being preferred. To obtain adequate data, the oscillationfrequency preferably is swept over several decades covering a range ofapproximately 0.15 rad/s to approximately 150 rad/s. For example,measurements can be taken at angular frequencies of approximately 0.147rad/s, approximately 0.216 rad/s, approximately 0.317 rad/s,approximately 0.467 rad/s, approximately 0.683 rad/s, approximately1.003 rad/s, approximately 1.472 rad/s, approximately 2.160 rad/s,approximately 3.171 rad/s, approximately 4.655 rad/s, approximately6.832 rad/s, approximately 10.028 rad/s, approximately 14.719 rad/s,approximately 21.604 rad/s, approximately 31.711 rad/s, approximately46.545 rad/s, approximately 68.319 rad/s, approximately 100.279 rad/s,and approximately 147.198 rad/s. Utilizing these exact frequencies isnot necessary, but utilizing a similar number of frequencies near thesevalues and spanning a similar range has been observed to producereliable results.

Once the out-of-phase viscosity (η″) and the dynamic viscosity (η′) forthe polymer have been measured, the average radius of the Cole-Cole plotcan be determined using the least squares approach as described above.To facilitate calculation of the average radius using the least squaresapproach, one of various software programs (e.g., Microsoft® Excel™ withthe solver add-in installed) can be used to fit the actual data. Forexample, when using Microsoft® Excel, a spreadsheet is created havingcolumns with equations for individual radius (r), individualout-of-phase viscosity (y), dynamic viscosity (x), and square of theerror (SE) at each dynamic viscosity and out-of-phase viscosity (x,y)pair. Then, the sum of the squared errors (SSE) is located in theworkbook cell set as the “Set Objective;” field to Minimize, whileconstants h and k are located in the workbook cells in the “By ChangingVariable Cells:” field. To avoid possible local minima, it is preferredto select “Use Multi-Start” under GRG Nonlinear, which requiresboundaries on h and k. For h, the boundary preferably is set to greaterthan zero but less than some number larger than the largest expected hvalue. Likewise for k, the boundary preferably is set to less than zerobut greater than some large negative number well more negative than theexpected k values.

Since these parameters are determined from the polymer melt, thepresence of the nucleating agent will not have any appreciable effectson the out-of-phase viscosity (η″), the dynamic viscosity (η′), or MeltFlow Index measured from the polyethylene polymer composition.Therefore, these parameters (and the Melt Relaxation Product) can bemeasured from the polyethylene polymer composition before it is combinedwith the bicyclo[2.2.1]heptane-2,3-dicarboxylic acid salt, or theparameters can be measured from a thermoplastic polymer compositioncomprising the polyethylene polymer composition and thebicyclo[2.2.1]heptane-2,3-dicarboxylic acid salt.

As noted above, the polyethylene polymer composition can comprise anysuitable polyethylene polymer or mixture of polyethylene polymersexhibiting the desired Melt Relaxation Product. Thus, the polyethylenepolymer composition can comprise a single polyethylene polymerexhibiting the desired Melt Relaxation Product. Alternatively, thepolyethylene polymer composition can comprise a mixture of two or morepolyethylene polymers in which the mixture exhibits the desired MeltRelaxation Product. In such a mixture, each polyethylene polymer canexhibit a Melt Relaxation Product falling within the desired range, butthis is not necessary. For example, a polyethylene polymer exhibiting arelatively high Melt Relaxation Product (e.g., greater than 50,000) canbe mixed with an appropriate amount of another polyethylene polymerhaving a lower Melt Relaxation Product (e.g., less than 50,000) to yielda polyethylene polymer composition exhibiting the desired MeltRelaxation Product.

Polyethylene polymers suitable for use in the polyethylene polymercomposition include polyethylene homopolymers and polyethylenecopolymers. Suitable polyethylene copolymers include copolymers ofethylene with one or more α-olefins. Suitable α-olefins include, but arenot limited to, 1-butene, 1-hexene, 1-octene, 1-decene, and4-methyl-1-pentene. The comonomer can be present in the copolymer in anysuitable amount, such as an amount of about 8% by weight or less (e.g.,less than about 5 mol %) or more preferably about 5% by weight or less(e.g., about 3 mol. % or less). As will be understood by those ofordinary skill in the art, the amount of comonomer suitable for thepolyethylene copolymer is largely driven by the end use for thecopolymer and the required or desired polymer properties dictated bythat end use.

The polyethylene polymers suitable for use in the thermoplastic polymercomposition can be produced by any suitable process. For example, thepolymers can be produced by a free radical process using very highpressures as described, for example, in U.S. Pat. No. 2,816,883 (Larcharet al.), but the polymers typically are produced in a “low pressure”catalytic process. In this context, the term “low pressure” is used todenote processes carried out at pressures less than 6.9 MPa (e.g., 1,000psig), such as 1.4-6.9 MPa (200-1,000 psig). Examples of suitable lowpressure catalytic processes include, but are not limited to, solutionpolymerization processes (i.e., processes in which the polymerization isperformed using a solvent for the polymer), slurry polymerizationprocesses (i.e., processes in which the polymerization is performedusing a hydrocarbon liquid in which the polymer does not dissolve orswell), gas-phase polymerization processes (e.g., processes in which thepolymerization is performed without the use of a liquid medium ordiluent), or a staged reactor polymerization process. The suitablegas-phase polymerization processes also include the so-called “condensedmode” or “super-condensed mode” processes in which a liquid hydrocarbonis introduced into the fluidized-bed to increase the absorption of theheat produced during the polymerization process. In these condensed modeand super-condensed mode processes, the liquid hydrocarbon typically iscondensed in the recycle stream and reused in the reactor. The stagedreactor processes can utilize a combination of slurry process reactors(tanks or loops) that are connected in series, parallel, or acombination of series or parallel so that the catalyst (e.g., chromiumcatalyst) is exposed to more than one set of reaction conditions. Stagedreactor processes can also be carried out by combining two loops inseries, combining one or more tanks and loops in series, using multiplegas-phase reactors in series, or a loop-gas phase arrangement. Becauseof their ability to expose the catalyst to different sets of reactorconditions, staged reactor processes are often used to producemultimodal polymers, such as those discussed below. Suitable processesalso include those in which a pre-polymerization step is performed. Inthis pre-polymerization step, the catalyst typically is exposed to thecocatalyst and ethylene under mild conditions in a smaller, separatereactor, and the polymerization reaction is allowed to proceed until thecatalyst comprises a relatively small amount (e.g., about 5% to about30% of the total weight) of the resulting composition. Thispre-polymerized catalyst is then introduced to the large-scale reactorin which the polymerization is to be performed.

The polyethylene polymers suitable for use in the thermoplastic polymercomposition can be produced using any suitable catalyst or combinationof catalysts. Suitable catalysts include transition metal catalysts,such as supported reduced molybdenum oxide, cobalt molybdate on alumina,chromium oxide, and transition metal halides. Chromium oxide catalyststypically are produced by impregnating a chromium compound onto aporous, high surface area oxide carrier, such as silica, and thencalcining it in dry air at 500-900° C. This converts the chromium into ahexavalent surface chromate ester or dichromate ester. The chromiumoxide catalysts can be used in conjunction with metal alkyl cocatalysts,such as alkyl boron, alkyl aluminum, alkyl zinc, and alkyl lithium.Supports for the chromium oxide include silica, silica-titania,silica-alumina, alumina, and aluminophosphates. Further examples ofchromium oxide catalysts include those catalysts produced by depositinga lower valent organochromium compound, such as bis(arene) Cr⁰, allylCr²⁺ and Cr³⁺, beta stabilized alkyls of Cr²⁺ and Cr⁴⁺, andbis(cyclopentadienyl) Cr²⁺, onto a chromium oxide catalyst, such asthose described above. Suitable transition metal catalysts also includesupported chromium catalysts such as those based on chromocene or asilylchromate (e.g., bi(trisphenylsilyl)chromate). These chromiumcatalysts can be supported on any suitable high surface area supportsuch as those described above for the chromium oxide catalysts, withsilica typically being used. The supported chromium catalysts can alsobe used in conjunction with cocatalysts, such as the metal alkylcocatalysts listed above for the chromium oxide catalysts. Suitabletransition metal halide catalysts include titanium (III) halides (e.g.,titanium (III) chloride), titanium (IV) halides (e.g., titanium (IV)chloride), vanadium halides, zirconium halides, and combinationsthereof. These transition metal halides are often supported on a highsurface area solid, such as magnesium chloride. The transition metalhalide catalysts are typically used in conjunction with an aluminumalkyl cocatalyst, such as trimethylaluminum (i.e., Al(CH₃)₃) ortriethylaluminum (i.e., Al(C₂H₅)₃). These transition metal halides mayalso be used in staged reactor processes. Suitable catalysts alsoinclude metallocene catalysts, such as cyclopentadienyl titanium halides(e.g., cyclopentadienyl titanium chlorides), cyclopentadienyl zirconiumhalides (e.g., cyclopentadienyl zirconium chlorides), cyclopentadienylhafnium halides (e.g., cyclopentadienyl hafnium chlorides), andcombinations thereof. Metallocene catalysts based on transition metalscomplexed with indenyl or fluorenyl ligands are also known and can beused to produce high density polyethylene polymers suitable for use inthe invention. The catalysts typically contain multiple ligands, and theligands can be substituted with various groups (e.g., n-butyl group) orlinked with bridging groups, such as —CH₂CH₂— or >SiPh₂. The metallocenecatalysts typically are used in conjunction with a cocatalyst, such asmethyl alum inoxane (i.e., (Al(CH₃)_(x)O_(y))_(n). Other cocatalystsinclude those described in U.S. Pat. No. 5,919,983 (Rosen et al.), U.S.Pat. No. 6,107,230 (McDaniel et al.), U.S. Pat. No. 6,632,894 (McDanielet al.), and U.S. Pat. No. 6,300,271 (McDaniel et al). Other “singlesite” catalysts suitable for use in producing polyethylene polymersinclude diimine complexes, such as those described in U.S. Pat. No.5,891,963 (Brookhart et al.).

The polyethylene polymer composition (and the polyethylene polymer(s)present in such composition) can have any suitable density. Suitabledensities range from about 880 kg/m³ to about 970 kg/m³. Preferably, thepolyethylene polymer composition has a density of about 940 kg/m³ ormore (e.g., about 940 kg/m³ to about 970 kg/m³). More preferably, thepolyethylene polymer composition has a density from about 945 kg/m³ toabout 967 kg/m³. In another preferred embodiment, the polyethylenepolymer composition has a density from about 955 kg/m³ to about 965kg/m³.

The polyethylene polymer composition (and the polyethylene polymer(s)present in such composition) can have any suitable Melt Flow Index(MFI). Preferably, the polyethylene polymer composition has an MFI ofabout 1 dg/min or more (e.g., about 2 dg/min or more). In anotherpreferred embodiment, the polyethylene polymer composition has an MFI ofabout 4 dg/min or more. Preferably, the polyethylene polymer compositionhas an MFI of about 80 dg/min or less. In another preferred embodiment,the polyethylene polymer composition has an MFI of about 60 dg/min orless. In yet another preferred embodiment, the polyethylene polymercomposition has an MFI of about 40 dg/min or less. Thus, in a series ofpreferred embodiments, the polyethylene polymer composition has an MFIof about 1 dg/min to about 80 dg/min (e.g., about 1 dg/min to about 60dg/min or about 1 dg/min to about 40 dg/min), about 2 dg/min to about 80dg/min (e.g., about 2 dg/min to about 60 dg/min or about 2 dg/min toabout 40 dg/min), or about 4 dg/min to about 80 dg/min (e.g., about 4dg/min to about 60 dg/min or about 4 dg/min to about 40 dg/min). TheMelt Flow Index of the polyethylene polymer composition preferably ismeasured in accordance with ASTM Standard D1238 at 190° C. using a 2.16kg load.

The thermoplastic polymer composition comprises a salt ofbicyclo[2.2.1]heptane-2,3-dicarboxylic acid. The two carboxylatemoieties of the bicyclo[2.2.1]heptane-2,3-dicarboxylate anion preferablyare located in the cis position relative to one another. Further, thetwo carboxylate moieties of the bicyclo[2.2.1]heptane-2,3-dicarboxylateanion preferably are in the endo position relative to the longest bridgeof the anion. Thus, in a preferred embodiment, the thermoplastic polymercomposition comprises a salt ofcis-endo-bicyclo[2.2.1]heptane-2,3-dicarboxylic acid (i.e.,(1R,2R,3S,4S)-bicyclo[2.2.1]heptane-2,3-dicarboxylic acid). The salt ofbicyclo[2.2.1]heptane-2,3-dicarboxylic acid can comprise any suitablecounterion for the bicyclo[2.2.1]heptane-2,3-dicarboxylate anion.Preferably, the counterion is selected from the group consisting ofalkali metal cations and alkaline earth metal cations. In anotherpreferred embodiment, the counterion is selected from the groupconsisting of alkaline earth metal cations. Most preferably, thecounterion is a calcium cation (i.e., a Ca²⁺ cation). Thus, in aparticularly preferred embodiment, the salt is calciumbicyclo[2.2.1]heptane-2,3-dicarboxylate, particularly calciumcis-endo-bicyclo[2.2.1]heptane-2,3-dicarboxylate (i.e., calcium(1R,2R,3S,4S)-bicyclo[2.2.1]heptane-2,3-dicarboxylate).

The salt of a bicyclo[2.2.1]heptane-2,3-dicarboxylic acid can be eithera hydrate (i.e., a crystalline solid with water of crystallization) or adehydrate (i.e., a crystalline solid without water of crystallization)Those skilled in the art will appreciate that the salt of abicyclo[2.2.1]heptane-2,3-dicarboxylic can also be a physical mixture ofa hydrate and a dehydrate. In a preferred embodiment, the salt of abicyclo[2.2.1]heptane-2,3-dicarboxylic acid is a dehydrate. In anotherpreferred embodiment, the salt of abicyclo[2.2.1]heptane-2,3-dicarboxylic acid is a hydrate, morepreferably a monohydrate. Those skilled in the art will recognize thatwhen starting with a monohydrate form, melt processing of the polymercomposition may remove at least some of the water of crystallization inthe bicyclo[2.2.1]heptane-2,3-dicarboxylic acid salt, which would yielda mixture of the monohydrate and dehydrate. Thus, in one preferredembodiment described above, the salt of abicyclo[2.2.1]heptane-2,3-dicarboxylic acid is a dehydrate prior to meltprocessing of the thermoplastic polymer composition. Accordingly, thecorresponding thermoplastic polymer composition is prepared by addingthe desired amount of the dehydrate of a salt of abicyclo[2.2.1]heptane-2,3-dicarboxylic acid to the polyethylene polymercomposition described above. In the other preferred embodiment, the saltof a bicyclo[2.2.1]heptane-2,3-dicarboxylic acid is a hydrate(preferably, a monohydrate) prior to melt processing of thethermoplastic polymer composition. Accordingly, the correspondingthermoplastic polymer composition is prepared by adding the desiredamount of the hydrate of a salt of abicyclo[2.2.1]heptane-2,3-dicarboxylic acid to the polyethylene polymercomposition described above. The addition of thebicyclo[2.2.1]heptane-2,3-dicarboxylic acid salt can be made by dryblending of the salt and the polyethylene polymer composition prior tomelt compounding or the salt can be added to the polyethylene polymercomposition while it is being melt processed, such as through a sidefeeder attached to an extruder.

The thermoplastic polymer composition can contain any suitable amount ofthe salt of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid. In a preferredembodiment, the thermoplastic polymer composition comprises about 50 ppmor more of the salt of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid. Inanother preferred embodiment, the thermoplastic polymer compositioncomprises about 100 ppm or more of the salt ofbicyclo[2.2.1]heptane-2,3-dicarboxylic acid. In yet another preferredembodiment, the thermoplastic polymer composition comprises about 200ppm or more of the salt of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid.In a preferred embodiment, the thermoplastic polymer compositioncomprises about 5,000 ppm or less of the salt ofbicyclo[2.2.1]heptane-2,3-dicarboxylic acid. In another preferredembodiment, the thermoplastic polymer composition comprises about 3,000ppm or less of the salt of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid.In yet another preferred embodiment, the thermoplastic polymercomposition comprises about 2,500 ppm or less of the salt ofbicyclo[2.2.1]heptane-2,3-dicarboxylic acid. Thus, in a series ofpreferred embodiments, the thermoplastic polymer composition comprisesabout 50 ppm to about 5,000 ppm (e.g., about 50 ppm to about 3,000 ppm,about 50 ppm to about 2,500 ppm, or about 50 to about 2,000 ppm), about100 ppm to about 5,000 ppm (e.g., about 100 ppm to about 3,000 ppm,about 100 ppm to about 2,500 ppm, or about 100 to about 2,000 ppm), orabout 200 to about 5,000 ppm (e.g., about 200 ppm to about 3,000 ppm,about 200 ppm to about 2,500 ppm, or about 200 to about 2,000 ppm) ofthe salt of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid.

In a preferred embodiment, the thermoplastic polymer compositioncomprises an acid scavenger in addition to the polyethylene polymercomposition and the salt of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid.Suitable acid scavengers include, but are not limited to, salts of fattyacids, hydrotalcite compounds, and mixtures thereof.

Thus, in one preferred embodiment, the thermoplastic polymer compositioncomprises a salt of a fatty acid in addition to the polyethylene polymercomposition and the salt of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid.In a preferred embodiment, the salt of a fatty acid is a salt of aC₁₂-C₂₂ fatty acid, more preferably a salt of a C₁₄-C₂₀ fatty acid or aC₁₆-C₁₈ fatty acid. In another preferred embodiment, the fatty acid is asaturated fatty acid (e.g., a saturated C₁₂-C₂₂ fatty acid, a saturatedC₁₄-C₂₀ fatty acid, or a saturated C₁₆-C₁₈ fatty acid). In aparticularly preferred embodiment, the salt of a fatty acid is a salt ofstearic acid. The salt of a fatty acid can comprise any suitablecounterion for the fatty acid anion. Preferably, the counterion isselected from the group consisting of alkali metal cations (e.g., asodium cation or a potassium cation), alkaline earth metal cations(e.g., a magnesium cation or a calcium cation), and Group 12 cations(e.g., a zinc cation). In a preferred embodiment, the counterion of thesalt of a fatty acid is a zinc cation. Thus, in a particularly preferredembodiment, the salt of a fatty acid is zinc stearate (i.e., the polymercomposition further comprises zinc stearate).

When present in the thermoplastic polymer composition, the salt of afatty acid can be present in any suitable amount. In a preferredembodiment, the thermoplastic polymer composition comprises about 50 ppmor more of the salt of a fatty acid. In another preferred embodiment,the thermoplastic polymer composition comprises about 100 ppm or more ofthe salt of a fatty acid. In yet another preferred embodiment, thethermoplastic polymer composition comprises about 200 ppm or more of thesalt of a fatty acid. In a preferred embodiment, the thermoplasticpolymer composition comprises about 5,000 ppm or less of the salt of afatty acid. In another preferred embodiment, the thermoplastic polymercomposition comprises about 3,000 ppm or less of the salt of a fattyacid. In yet another preferred embodiment, the thermoplastic polymercomposition comprises about 2,500 ppm or less of the salt of a fattyacid. Thus, in a series of preferred embodiments, the thermoplasticpolymer composition comprises about 50 ppm to about 5,000 ppm (e.g.,about 50 ppm to about 3,000 ppm, about 50 ppm to about 2,500 ppm, orabout 50 to about 2,000 ppm), about 100 ppm to about 5,000 ppm (e.g.,about 100 ppm to about 3,000 ppm, about 100 ppm to about 2,500 ppm, orabout 100 to about 2,000 ppm), or about 200 to about 5,000 ppm (e.g.,about 200 ppm to about 3,000 ppm, about 200 ppm to about 2,500 ppm, orabout 200 to about 2,000 ppm) of the salt of a fatty acid.

When present in the thermoplastic polymer composition, the salt of afatty acid can be present in any suitable relative amount with respectto the amount of the salt of a bicyclo[2.2.1]heptane-2,3-dicarboxylicacid. In a preferred embodiment, the two are present in thethermoplastic polymer composition in a mass ratio of about 5:1 to about1:5 based on the mass of the salt of abicyclo[2.2.1]heptane-2,3-dicarboxylic acid to the mass of the salt of afatty acid. In another preferred embodiment, the two are present in thethermoplastic polymer composition in a mass ratio of about 3:1 to about1:3 based on the mass of the salt of abicyclo[2.2.1]heptane-2,3-dicarboxylic acid to the mass of the salt of afatty acid. In yet another preferred embodiment, the two are present inthe thermoplastic polymer composition in a mass ratio of about 2:1 toabout 1:2 based on the mass of the salt of abicyclo[2.2.1]heptane-2,3-dicarboxylic acid to the mass of the salt of afatty acid. More preferably, the two are present in the thermoplasticpolymer composition in a mass ratio of about 2:1 to about 1:1 based onthe mass of the salt of a bicyclo[2.2.1]heptane-2,3-dicarboxylic acid tothe mass of the salt of a fatty acid. Most preferably, the two arepresent in the thermoplastic polymer composition in a mass ratio ofabout 2:1 based on the mass of the salt of abicyclo[2.2.1]heptane-2,3-dicarboxylic acid to the mass of the salt of afatty acid.

In another preferred embodiment, the thermoplastic polymer compositioncomprises a hydrotalcite compound in addition to the polyethylenepolymer composition and the salt ofbicyclo[2.2.1]heptane-2,3-dicarboxylic acid. Suitable hydrotalcitecompounds can be either naturally occurring or synthetically produced,though synthetically produced materials are generally preferred.Suitable synthetic hydrotalcite compounds include, but are not limitedto, the line of materials sold by Kyowa Chemical Industry Co., Ltd.under the “DHT” name, such as the DHT-4A® hydrotalcite-like material.When present in the thermoplastic polymer composition, the hydrotalcitecompound can be present in any suitable amount, including any of theamounts and/or ratios described above for the salt of a fatty acid.Further, the thermoplastic polymer composition can, in certainembodiments, comprise both a salt of a fatty acid and a hydrotalcitecompound.

The thermoplastic polymer composition described herein can be used toproduce any suitable article or product. Suitable products include, butare not limited to, medical devices (e.g., pre-filled syringes forretort applications, intravenous supply containers, and blood collectionapparatus), food packaging, liquid containers (e.g., containers fordrinks, medications, personal care compositions, shampoos, and thelike), apparel cases, microwavable articles, shelving, cabinet doors,mechanical parts, automobile parts, sheets, pipes, tubes, rotationallymolded parts, blow molded parts, films, fibers, and the like. Thethermoplastic polymer composition can be formed into the desired articleby any suitable technique, such as injection molding, injectionrotational molding, blow molding (e.g., injection blow molding orinjection stretch blow molding), extrusion (e.g., sheet extrusion, filmextrusion, cast film extrusion, or foam extrusion), extrusion blowmolding, thermoforming, rotomolding, film blowing (blown film), filmcasting (cast film), and the like. The thermoplastic polymer compositiondisclosed herein is believed to be particularly well-suited for use ininjection molding and cast film processes, with injection moldingprocesses being particularly preferred.

The disclosed thermoplastic polymer composition is believed to bewell-suited for use in injection molding and cast film processes becauseof its exceptionally improved (i.e., lower) water vapor and oxygentransmission rates as compared to the unnucleated polymer as well asnucleated polymers that do not exhibit the described physical properties(e.g., density, Melt Relaxation Product, Melt Flow Index, etc.). Forexample, a cast film made from the disclosed thermoplastic polymercomposition has been observed to exhibit markedly lower water vapor andoxygen transmission rates than a similar cast film made from a nucleatedpolymer that does not exhibit the desired Melt Relaxation Product.Further, injection molded articles made from the disclosed thermoplasticpolymer composition have been observed to exhibit markedly lower watervapor and oxygen transmission rates than a similar injection moldedarticles made from a nucleated polymer that does not exhibit the desiredMelt Relaxation Product. As described noted above, this result isbelieved to be attributable to the selection of a polyethylene polymercomposition that exhibits sufficient melt relaxation to maximize thenucleating effects of the bicyclo[2.2.1]heptane-2,3-dicarboxylic acidsalt.

Thus, in a second embodiment, the invention provides a method for amethod for producing an injection molded article from a thermoplasticpolymer composition. The method comprises the steps of:

(a) providing a thermoplastic polymer composition comprising (i) apolyethylene polymer composition having a Melt Relaxation Product of50,000 or less; and (ii) a salt ofbicyclo[2.2.1]heptane-2,3-dicarboxylic acid;

(b) heating the thermoplastic polymer composition to a temperaturesufficient to melt the thermoplastic polymer composition so that it maybe injected into a mold, the mold having a mold cavity defining thedimensions of an article;

(c) injecting the molten thermoplastic polymer composition into the moldcavity;

(d) allowing the molten thermoplastic polymer composition in the moldcavity to cool and solidify thereby forming an injection molded article;and

(e) opening the mold and ejecting the article from the mold cavity.

The thermoplastic polymer composition utilized in the method of thissecond embodiment can be any of the thermoplastic polymer compositionsdescribed above. The apparatus used in practicing the method of theinvention can be any suitable injection molding apparatus.

In the method described above, the thermoplastic polymer composition canbe heated to any suitable temperature that melts the thermoplasticpolymer composition and allows it to be injected into the mold cavity.The temperature to which the thermoplastic polymer composition is heateddoes not have a significant effect on the nucleation performance of thebicyclo[2.2.1]heptane-2,3-dicarboxylate salt, but higher temperaturesmay promote greater and faster melt relaxation which could, in turn,improve nucleation performance to some degree. However, the temperatureto which the thermoplastic polymer composition is heated should not beexcessively high so as to cause excessive “flashing” (i.e., melt leakagefrom the seam of the mold). Preferably, the thermoplastic polymercomposition is heated to a temperature of about 150° C. to about 220° C.The thermoplastic polymer composition can initially be heated to atemperature of about 150° C. to about 170° C. in the feed throat of theextruder followed by heating to a temperature of about 180° C. to about220° C. in the final zones of the extruder. Once heated to the desiredtemperature, the molten thermoplastic polymer composition preferably ismaintained at the desired temperature until it is injected into the moldcavity.

In a third embodiment, the invention also provides a method forproducing a film from a thermoplastic polymer composition. The methodcomprises the steps of:

(a) providing a thermoplastic polymer composition comprising (i) apolyethylene polymer composition having a Melt Relaxation Produce of50,000 or less; and (ii) a salt ofbicyclo[2.2.1]heptane-2,3-dicarboxylic acid;

(b) heating the thermoplastic polymer composition to a temperaturesufficient to melt the thermoplastic polymer composition so that it maybe extruded through a die;

(c) extruding the molten thermoplastic polymer composition through a diehaving a slot-shaped die orifice to form a film exiting the die orifice;

(d) passing the film exiting the die orifice over a cooled surface tosolidify the thermoplastic polymer composition; and

(e) collecting the film.

The thermoplastic polymer composition utilized in the method of thissecond embodiment can be any of the thermoplastic polymer compositionsdescribed above. The apparatus used in practicing the method of theinvention can be any suitable cast film apparatus. For example, the castfilm machine can be equipped with a single extruder and die thatproduces a monolayer film. Alternatively, the cast film machine can beequipped with one or more extruders and an appropriate die feedblockadapted to produce and combine multiple separate layers in the melt intoa single film. The films produced by such a cast film machine would bemultilayer films. When a multilayer film is produced, the thermoplasticpolymer composition of the invention can be used to produce any one ormore layers of the multilayer film. In other words, the method describedabove encompasses methods of producing multilayer films in which alllayers of the film are produced using the recited thermoplastic polymercomposition as well as multilayer films in which the recitedthermoplastic polymer composition is used to produce at least one layerof the multilayer film and one or more additional polymer compositionsare used to produce the remaining layers of the multilayer film.

In the method described above, the thermoplastic polymer composition canbe heated to any suitable temperature that melts the thermoplasticpolymer composition and allows it to be extruded through the die. Thetemperature to which the thermoplastic polymer composition is heateddoes not have a significant effect on the nucleation performance of thebicyclo[2.2.1]heptane-2,3-dicarboxylate salt, but higher temperaturesmay promote greater and faster melt relaxation which could, in turn,improve nucleation performance to some degree. However, the temperatureto which the thermoplastic polymer composition is heated should not beexcessively high, which may lower the viscosity of the molten polymercomposition to a point where the quality of the cast film suffers.Preferably, the thermoplastic polymer composition is heated to atemperature of about 150° C. to about 220° C. The thermoplastic polymercomposition can initially be heated to a temperature of about 150° C. toabout 170° C. in the feed throat of the extruder followed by heating toa temperature of about 180° C. to about 220° C. in the final zones ofthe extruder, transfer line section(s), and slot die. Once heated to thedesired temperature, the molten thermoplastic polymer compositionpreferably is maintained at the desired temperature until it is extrudedthrough the die orifice. Depending on polymer characteristics, those ofordinary skill in the art of cast film production will recognize theneed for temperature adjustments to maintain an appropriate compromisebetween mass output, system back pressures, and film stability.

The molten polymer can be fed directly from the extruder to the dieorifice. Alternatively, the molten polymer can be fed from the extruderinto a melt pump which is connected to the die or die feedblock.Suitable melt pumps preferably are positive displacement devices thatproduce a consistent flow of molten polymer to the die or die feedblockregardless of the discharge pressure of the extruder. The use of a meltpump can provide steadier short-term mass output than an extruder alone,which in turn can minimize machine direction thickness variation in thecast film (i.e., “surging”).

After exiting the die, the film is passed over a cooled surface tosolidify the thermoplastic polymer composition. This cooled surfacetypically is one or more quenching rolls that are cooled, for example,by circulating chilled water or another cooling agent through theinterior volume of the roll. In some applications, a vacuum box can beused to remove entrained air that would otherwise be trapped between thequenching roll surface and the film. Such entrained air acts as thermalinsulation, so reducing or eliminating the amount of entrained air willincrease the speed at which the film is cooled to the desiredtemperature.

The cooled film described above can be collected in any suitable manner.For example, the film is generally rolled by a winder, such as a surfacewinder, turret or center winder, or a center/surface winder.

The following examples further illustrate the subject matter describedabove but, of course, should not be construed as in any way limiting thescope thereof.

Example 1

The following example demonstrates the production of and properties ofseveral thermoplastic polymer compositions according to the invention.

Several commercially available high-density polyethylene resins weretested to determine their Melt Flow Index (MFI) and the average radiusof their Cole-Cole plot (r_(avg)). The Melt Relaxation Product (MRP) ofeach resin was then calculated. The results of these measurements andthe calculations are set forth in Table 1 below.

The MFI of each polyethylene polymer, which is reported in units ofdecigrams per minute (dg/min), was measured in accordance with ASTMStandard D1238 at 190° C. using a 2.16 kg load. The average radius ofthe Cole-Cole plot (r_(avg)) was determined in accordance with thegeneral procedure described above. In particular, the dynamic viscosity(η′) and out-of-phase viscosity (η″) were measured using a TAInstruments ARES G2 rotational rheometer equipped with 25-mm parallelplates which were set at 1.1 mm gap. A compression molded disk of thepolymer was placed on the bottom plate of the rheometer and allowed tomelt at the measurement temperature of 140° C. The top and bottom plateswere then set at the desired 1.1 mm gap and any excess molten polymerprotruding beyond the disk perimeter was trimmed. Measurements of theviscosity were then taken at angular frequencies of approximately 0.147,0.216, 0.317, 0.467, 0.683, 1.003, 1.472, 2.160, 3.171, 4.655, 6.832,10.028, 14.719, 21.604, 31.711, 46.545, 68.319, 100.279, and 147.198rad/s. These measurements yielded dynamic viscosity (η′) andout-of-phase viscosity (η″) values (among the outputs typicallyavailable in modern rheometers) that were then plotted to generate aCole-Cole plot with the dynamic viscosity (η′) as the x axis and theout-of-phase viscosity (η″) as the y axis.

To determine the average radius of the Cole-Cole plot for each resin,the measured data were fit to the following cartesian equation for acircle using the least squares approach:r ²=(x−h)²+(y−k)².

In the equation above, x corresponds to the dynamic viscosity (η′)value, and y corresponds to the out-of-phase viscosity (η″) value. Thevariables h and k represent the offset of the center of the circle fromthe origin of the Cole-Cole plot. Due to the nature of the complexviscosity, the value of h is a positive number, and the value of k is anegative number. The actual fit of the data was performed usingMicrosoft® Excel™ with the solver add-in installed. Columns were builtwith equations for individual r, individual y, individual x, and squareof the error (SE) at each (x,y) pair generated at each strain rate.Then, the sum of the squared errors (SSE) was located in the workbookcell set as the “Set Objective:” field to Minimize, while constants hand k were located in the workbook cells in the “By Changing VariableCells:” field. To avoid possible local minima, GRG Nonlinear was set to“Use Multi-Start.” The boundary for h was set to greater than zero butless than some number larger than the largest expected h value. Theboundary for k was set to less than zero but greater than some largenegative number well more negative than the expected k values. After thefit was run and the SSE was minimized, the radius values for each x,ypair of the Cole-Cole plot were averaged, and the resulting value wasreported as the average radius of the Cole-Cole plot (r_(avg)) for thepolymer.

TABLE 1 Density, Melt Flow Index, average radius of the Cole-Cole plot(r_(avg)), and Melt Relaxation Product values for several commercialHDPE polymers. Melt Relaxation density MFI Product HDPE Polymer (kg/m³)(dg/min) r_(avg) (MRP) Dow DMDA-8904 952 4.4 7,550 33,200 Nova Sclair2607 947 4.8 5,280 25,300 Nova Sclair 2807 954 6.7 4,530 30,400 DowDMDA-8007 965 8.3 2,980 24,700 ExxonMobil HD 6719.17 952 19 1,320 25,100Dowlex IP 40 952 40 1,400 56,000

Several polymer compositions were made with the aforementioned HDPEpolymers to investigate the relationship between the Melt RelaxationProduct of a polymer and the nucleation efficiency of thebicyclo[2.2.1]heptane-2,3-dicarboxylate salt. To facilitate mixing thebicyclo[2.2.1]heptane-2,3-dicarboxylate salt with each HDPE polymer, amasterbatch was produced by combining 240.0 g of calciumbicyclo[2.2.1]heptane-2,3-dicarboxylate, 120.0 g of zinc stearate, 90 gof DHT-4V, 0.90 g of Irganox 1010, 2.1 g of Irgafos 168, and 5547.0 g ofNova Sclair 2908 HDPE polymer. The mixture was transferred to and mixedin a 30-liter Henschel high intensity mixer for 3.0 minutes at 1200 rpm.The resulting mixture was then compounded using a Leistritz 27-mmcorotating twin screw extruder at 18 kg/hr with a screw speed of 400rpm, the first zone set to 100° C., and other zones ranging from165-175° C. The resulting masterbatch, which contained four percent byweight calcium bicyclo[2.2.1]heptane-2,3-dicarboxylate, will hereafterbe referred to as “Masterbatch 1.”

The polymer compositions containing thebicyclo[2.2.1]heptane-2,3-dicarboxylate salt were prepared by twin screwcompounding/pelletizing a dry blend of Masterbatch 1 and the HDPEpolymer on a Leistritz 18-mm corotating twin screw extruder at 3.5 kg/hrusing a screw speed of approximately 500 rpm. The first zone was set to160° C. with following zones varying between 145-155° C.

Portions of the non-nucleated HDPE polymer and the nucleated HDPEpolymer were then molded into shrinkage plaques (2.0 mm×60.0 mm×60.0 mm)according to ISO 294 with a 55-ton Arburg injection molding unit anddual cavity mold. Shrinkage measurements on the plaques were taken inaccordance with ISO 294. The results of the shrinkage measurements areset forth in Table 2 below.

TABLE 2 Transverse direction (TD) shrinkage results for Samples 1-16.HDPE Nucleator MFI % TD Sample Resin (ppm) (dg/min) MRP Shrinkage 1DMDA- 0 8.3 24,700 1.60 8007 2 DMDA- 200 0.37 8007 3 DMDA- 300 0.34 80074 DMDA- 600 0.29 8007 5 DMDA- 900 0.27 8007 6 DMDA- 1200 0.26 8007 7Sclair 2807 0 6.7 30,400 1.49 8 Sclair 2807 900 0.26 9 DMDA- 0 4.433,200 1.78 8904 10 DMDA- 900 0.22 8904 11 Sclair 2607 0 4.8 25,300 1.6112 Sclair 2607 900 0.18 13 HD 6719.17 0 19 25,100 1.65 14 HD 6719.17 9000.51 15 Dowlex IP 0 40 56,000 1.54 40 16 Dowlex IP 800 0.82 40

For the bicyclo[2.2.1]heptane-2,3-dicarboxylate salt used as thenucleating agent in these samples, low transverse direction shrinkagecompared to the control, non-nucleated polymer is an indicator of goodnucleation efficiency of the polymer. As can be seen from the data inTable 2, the calcium bicyclo[2.2.1]heptane-2,3-dicarboxylate was able tonucleate all of the HDPE polymers as evidenced by the reduction intransverse direction shrinkage. However, the reduction in shrinkage forSample 16 was much lower than the reduction observed for Samples 2-6, 8,10, 12, and 14. This data shows that the calciumbicyclo[2.2.1]heptane-2,3-dicarboxylate was not able to nucleate thisparticular HDPE polymer (i.e., the Dowlex IP 40 used in Sample 16) aswell as the other HDPE polymers. As shown in Tables 1 and 2, the DowlexIP 40 polymer used in making Sample 16 has an MRP greater than 50,000,whereas the polymers used in making Samples 2-6, 8, 10, 12, and 14 hadMRP less than 50,000 (e.g., less than 35,000).

Portions of the non-nucleated HDPE polymer and the nucleated HDPEpolymer were also molded into barrier plaques with an end-gate squaremold with dimensions of 1.0-mm thick×4.0-inch (101.6 mm) width×4.0-inch(101.6 mm) breadth on a Husky 90-ton injection molding unit. Extruderzones from feed to end were 230/250/230° C., nozzle 250° C., and moldcoolant 45° C. Injection linear velocity was 60 mm/second. Total cycletime was 19.7 seconds, with cooling time of 10.0 seconds, and pressureof 900 psi. Water vapor transmission rate (WVTR) measurements on theresulting barrier plaques were taken in accordance with ASTM F 1249,with the results normalized to thickness (yielded nWVTR). Conventionaloxygen transmission rate (OTR) measurements were also taken on someplaques in accordance with ASTM D 3985 (dry, 23° C.), but with house lowdew point air rather than 100% oxygen insult. The measurements weretaken with an Illinois Instruments Model 8001 oxygen permeationanalyzer. The initial OTR measurements were normalized to thickness. Thenormalized OTR (nOTR) are reported in units of cc*mil/m²/24-hr/0.209 atm02. The results of the nWVTR and nOTR measurements are set forth inTable 3 below.

TABLE 3 Normalized water vapor transmission rates (nWVTR), percentchange in nWVTR (% Δ), normalized oxygen transmission rates (nOTR), andpercent change in nOTR (% Δ) for Samples 1-16. nOTR Nucleator MFI (0.209Sample HDPE Resin (ppm) (dg/min) MRP nWVTR % Δ atm) % Δ 1 DMDA-8007 08.3 24,700 4.61 359 2 DMDA-8007 200 2.76 −40 212 −41 3 DMDA-8007 3002.61 −43 161 −55 4 DMDA-8007 600 2.49 −46 147 −59 5 DMDA-8007 900 2.33−49 144 −60 6 DMDA-8007 1200 2.33 −49 141 −61 7 Sclair 2807 0 6.7 30,4005.80 8 Sclair 2807 900 2.91 −50 9 DMDA-8904 0 4.4 33,200 5.90 10DMDA-8904 900 3.53 −40 11 Sclair 2607 0 4.8 25,300 6.72 532 12 Sclair2607 900 3.42 −49 235 −56 13 HD 6719.17 0 19 25,100 5.55 426 14 HD6719.17 900 3.08 −45 209 −51 15 Dowlex IP 0 40 56,000 4.49 40 16 DowlexIP 800 3.76 −16 40

The data in Table 3 show that the calciumbicyclo[2.2.1]heptane-2,3-dicarboxylate was able to nucleate all of theHDPE polymers as evidenced by a measured reduction in nWVTR. However,the reduction in nWVTR for Sample 16 was much lower than the reductionobserved for Samples 2-6, 8, 10, 12, and 14. Indeed, the reduction forSample 16 was only about one third of the reduction observed for theother samples. This data shows that the calciumbicyclo[2.2.1]heptane-2,3-dicarboxylate was not able to nucleate theDowlex IP 40 used in Sample 16 as well as the other HDPE polymers. Asnoted above, the Dowlex IP 40 polymer used in making Sample 16 has anMRP greater than 50,000, whereas the polymers used in making Samples2-6, 8, 10, 12, and 14 had MRP less than 50,000 (less than 35,000).

Decreases in transverse direction shrinkage and WVTR are directlyrelated to nucleation of the polyethylene polymer composition by thebicyclo[2.2.1]heptane-2,3-dicarboxylate salt. Thus, the differencesbetween these two groups' results show that thebicyclo[2.2.1]heptane-2,3-dicarboxylate salt is more effective atnucleating those polymers and polymer blends with a Melt RelaxationProduct of 50,000 or less. This is surprising because nothing known inthe art suggests that nucleation with abicyclo[2.2.1]heptane-2,3-dicarboxylate salt is dependent upon thesepolymer characteristics. However, as explained above, the inventorsbelieve this difference is due to the lower degree of melt relaxationexhibited by polymers having a Melt Relaxation Product greater than50,000. In such polymers, the polymer melt relaxes slowly, resulting inappreciable amounts of strain-induced, self-nucleation rather thannucleation by the bicyclo[2.2.1]heptane-2,3-dicarboxylate salt.

Example 2

The following example demonstrates the production of and properties ofseveral thermoplastic polymer compositions.

Several polymer compositions were made by mixing various amounts of DowUnival® DMDH-6400 NT 7 HDPE polymer with the ExxonMobil HD 6719.17 HDPEpolymer used in Example 1. Non-nucleated controls were made by mixingthe desired amounts of DMDH-6400 polymer and HD 6719.17 polymer with 2%of Sclair 2908 HDPE resin (the carrier used in making the masterbatchdescribed in Example 1). Nucleated samples were made by mixing thedesired amounts of DMDH-6400 polymer and HD 6719.17 polymer with 2% ofMasterbatch 1 described in Example 1. The percentages of DMDH-6400polymer and HD 6719.17 polymer in each sample are set forth in Table 4below. The polymer blends were compounded with a Leistritz 18-mmcorotating twin screw extruder at a screw speed of 500 rpm, a feed rateof 4.0 kg/hr, and barrel temperature setpoints ranging from 155-165° C.

Each polymer composition was molded into barrier plaques as described inExample 1. The normalized oxygen transmission rate (nOTR) for eachplaque was also measured as described in Example 1. The results of thesemeasurements are set forth in Table 4 below.

TABLE 4 Melt Flow Index (MFI), average radius of the Cole-Cole plot(r_(avg)), Melt Relaxation Product (MRP), and normalized oxygentransmission rates (nOTR), and percent change in nOTR (Δ %) for Samples17-22. Nucleator MFI nOTR Sample Polymers (%) (ppm) (dg/min) r_(avg) MRP0.209 atm % Δ 17 DMDH-6400 (30) 0 8.1 21,950 177,800 409 HD 6719.17 (68)Sclair 2908 (2) 18 DMDH-6400 (30) 800 307 −25 HD 6719.17 (68) MB Ex. 19(2) 19 DMDH-6400 (20) 0 10.0 11,810 118,100 361 HD 6719.17 (78) Sclair2908 (2) 20 DMDH-6400 (20) 800 275 −24 HD 6719.17 (78) MB Ex. 19 (2) 21DMDH-6400 (10) 0 14.1 4,670 65,800 351 HD 6719.17 (88) Sclair 2908 (2)22 DMDH-6400 (10) 800 260 −26 HD 6719.17 (88) MB Ex. 19 (2)

As can be seen from the data in Table 4, the reductions in nOTR arerelatively modest for all of the polymer blends. Indeed, the reductionsin nOTR observed for Samples 18, 20, and 22 were only about half of thereductions observed for Samples 2-6, 12, and 14 from Example 1. Further,the data in Table 4 show that Samples 17-22 had MRP significantly higherthan 50,000. These high MRP values are indicative of insufficient meltrelaxation in the polymer, which, as noted above, impedes nucleation ofthe polymer by the bicyclo[2.2.1]heptane-2,3-dicarboxylate salt.

Example 3

The following example demonstrates the production of and properties ofseveral thermoplastic polymer compositions.

Several polymer compositions were made using the HD 6719.17 HDPE polymerdescribed above. The polymer compositions were made by compounding theHDPE polymer with increasing amounts of peroxide, specifically2,5-dimethyl-2,5-di-(t-butylperoxy)hexane (Varox® DBPH). It is generallyaccepted that treating a copolymer HDPE polymer with peroxide willincrease long chain branching (LCB), with an understanding that someshort chain branching (SCB) could also occur. The branching contributesto at least some molecular weight increase (and MI decrease), andtypically at least some broadening of molecular weight distribution.Both of these effects should increase the average radius of theCole-Cole plot, which should also increase the Melt Relaxation Product(MRP). Thus, this series of experiments explores the effect ofincreasing the MRP for a given polyethylene polymer composition.

The polymer compositions were produced by adding the desired amount ofperoxide (DBPH) to 4 kg of HD 6719.17 powder that had been ground fromthe commercially available pellets in an attrition mill. In particular,the polymer powder was charged into a Hobart mixer and mixing wasstarted. The DBPH, which is a liquid at room temperature, was slowlyadded dropwise until the desired amount of DBPH was added and mixingcontinued for five minutes. The resulting mixture was then extruded andpelletized with a Deltaplast single screw extruder (one inch (2.54 cm)diameter, L/D 30, Maddock mixing section, flat barrel profile of 210°C.) interfaced to a strand pelletizer. A screen pack stack to include150 mesh was also used to raise back pressure and cause moreslippage/mixing in the extruder, thereby ensuring that the peroxide wasthoroughly incorporated into the polymer. The collected pellets weretumble blended to more fully homogenize the sample before furtherprocessing. The amount of peroxide (DBPH) and calciumbicyclo[2.2.1]heptane-2,3-dicarboxylate used in making each polymercomposition is set forth in Table 5 below.

Portions of the resulting pelletized polymer compositions were moldedinto barrier plaques as described in Example 1. Other portions of thecompositions were dry blended with 2.2% of Masterbatch 1 described inExample 1 to give nucleated compositions containing 880 ppm nucleator,and the resulting nucleated compositions were also molded into barrierplaques as in Example 1. The barrier plaques were then analyzed todetermine normalized oxygen transmission rates (nOTR) using theprocedure described in Example 1. The results of these analyses are setforth in Table 5 below.

TABLE 5 DBPH concentration, nucleator concentration, Melt Flow Index(MFI), average radius of the Cole-Cole Plot (r_(avg)), Melt RelaxationProduct (MRP), normalized oxygen transmission rate (nOTR), and percentchange in nOTR (% Δ) for Samples 23-34. DBPH Nucleator MFI nOTR Sample(ppm) (ppm) (dg/min) r_(avg) MRP 0.209 atm % Δ 23 60 0 16.6 1,900 31,500447 24 60 880 248 −45 25 100 0 15.4 2,230 34,300 442 26 100 880 239 −4627 160 0 13.5 2,770 37,400 431 28 160 880 247 −43 29 220 0 10.4 3,74038,900 434 30 220 880 245 −44 31 280 0 8.6 4,900 42,100 423 32 280 880243 −43 33 340 0 7.1 6,320 44,900 413 34 340 880 257 −38

The data in Table 5 show that increasing amounts of peroxide resulted ina decrease in the melt flow index (MFI) and an increase in the averageradius of the Cole-Cole plot (r_(avg)). The increase in r_(avg) was ofgreater magnitude than the decrease in MFI, which resulted in anincrease in the Melt Relaxation Product (MRP). An examination of thenOTR data for Samples 24, 26, 28, 30, 32, and 34 shows that themagnitude of the decrease in nOTR relative to the non-nucleated controlgenerally decreases as the MRP increases. However, even at an MRP of44,900, Sample 34 still showed a 38% decrease in nOTR relative to thecontrol, which indicates that this polymer still exhibited sufficientmelt relaxation for nucleation by thebicyclo[2.2.1]heptane-2,3-dicarboxylate salt to predominate over anystrain-induced, self-nucleation.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the subject matter of this application (especiallyin the context of the following claims) are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The terms “comprising,” “having,”“including,” and “containing” are to be construed as open-ended terms(i.e., meaning “including, but not limited to,”) unless otherwise noted.Recitation of ranges of values herein are merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate the subject matter of theapplication and does not pose a limitation on the scope of the subjectmatter unless otherwise claimed. No language in the specification shouldbe construed as indicating any non-claimed element as essential to thepractice of the subject matter described herein.

Preferred embodiments of the subject matter of this application aredescribed herein, including the best mode known to the inventors forcarrying out the claimed subject matter. Variations of those preferredembodiments may become apparent to those of ordinary skill in the artupon reading the foregoing description. The inventors expect skilledartisans to employ such variations as appropriate, and the inventorsintend for the subject matter described herein to be practiced otherwisethan as specifically described herein. Accordingly, this disclosureincludes all modifications and equivalents of the subject matter recitedin the claims appended hereto as permitted by applicable law. Moreover,any combination of the above-described elements in all possiblevariations thereof is encompassed by the present disclosure unlessotherwise indicated herein or otherwise clearly contradicted by context.

What is claimed is:
 1. A thermoplastic polymer composition comprising:(a) a polyethylene polymer composition having a Melt Relaxation Productof 50,000 or less; and (b) calciumbicyclo[2.2.1]heptane-2,3-dicarboxylate.
 2. The thermoplastic polymercomposition of claim 1, wherein the polyethylene polymer composition hasa Melt Relaxation Product of 45,000 or less.
 3. The thermoplasticpolymer composition of claim 1, wherein the polyethylene polymercomposition has a Melt Flow Index at 190° C. of about 1 dg/min to about80 dg/min.
 4. The thermoplastic polymer composition of claim 1, whereinthe calcium bicyclo[2.2.1]heptane-2,3-dicarboxylate is a salt ofcis-endo-bicyclo[2.2.1]heptane-2,3-dicarboxylic acid.
 5. Thethermoplastic polymer composition of claim 1, wherein the thermoplasticpolymer composition contains about 100 ppm to about 3,000 ppm of thecalcium bicyclo[2.2.1]heptane-2,3-dicarboxylate.
 6. The thermoplasticpolymer composition of claim 1, wherein the thermoplastic polymercomposition further comprises an acid scavenger selected from the groupconsisting of salts of C₁₂-C₂₂ fatty acids, hydrotalcite compounds, andmixtures thereof.
 7. The thermoplastic polymer composition of claim 6,wherein the thermoplastic polymer composition contains about 100 ppm toabout 3,000 ppm of the salt of the acid scavenger.
 8. A method forproducing an injection molded article, the method comprising the stepsof: (a) providing a thermoplastic polymer composition comprising (i) apolyethylene polymer composition having a Melt Relaxation Product of50,000 or less; and (ii) calciumbicyclo[2.2.1]heptane-2,3-dicarboxylate; (b) heating the thermoplasticpolymer composition to a temperature sufficient to melt thethermoplastic polymer composition so that it may be injected into amold, the mold having a mold cavity defining the dimensions of anarticle; (c) injecting the molten thermoplastic polymer composition intothe mold cavity; (d) allowing the molten thermoplastic polymercomposition in the mold cavity to cool and solidify thereby forming aninjection molded article; and (e) opening the mold and ejecting thearticle from the mold cavity.
 9. The method of claim 8, wherein thepolyethylene polymer composition has a Melt Relaxation Product of 45,000or less.
 10. The method of claim 8, wherein the polyethylene polymercomposition has a Melt Flow Index at 190° C. of about 1 dg/min to about80 dg/min.
 11. The method of claim 8, wherein the calciumbicyclo[2.2.1]heptane-2,3-dicarboxylate is a salt ofcis-endo-bicyclo[2.2.1]heptane-2,3-dicarboxylic acid.
 12. The method ofclaim 8, wherein the thermoplastic polymer composition contains about100 ppm to about 3,000 ppm of the calciumbicyclo[2.2.1]heptane-2,3-dicarboxylate.
 13. The method of claim 8,wherein the thermoplastic polymer composition further comprises an acidscavenger selected from the group consisting of salts of C₁₂-C₂₂ fattyacids, hydrotalcite compounds, and mixtures thereof.
 14. The method ofclaim 13, wherein the polymer composition contains about 100 ppm toabout 3,000 ppm of the salt of the acid scavenger.
 15. A method forproducing a film, the method comprising the steps of: (a) providing athermoplastic polymer composition comprising (i) a polyethylene polymercomposition having a Melt Relaxation Produce of 50,000 or less; and (ii)calcium bicyclo[2.2.1]heptane-2,3-dicarboxylate; (b) heating thethermoplastic polymer composition to a temperature sufficient to meltthe thermoplastic polymer composition so that it may be extruded througha die; (c) extruding the molten thermoplastic polymer compositionthrough a die having a slot-shaped die orifice to form a film exitingthe die orifice; (d) passing the film exiting the die orifice over acooled surface to solidify the thermoplastic polymer composition; and(e) collecting the film.
 16. The method of claim 15, wherein thepolyethylene polymer composition has a Melt Relaxation Product of 45,000or less.
 17. The method of claim 15, wherein the polyethylene polymercomposition has a Melt Flow Index at 190° C. of about 1 dg/min to about80 dg/min.
 18. The method of claim 15, wherein the thermoplastic polymercomposition comprises calcium bicyclo[2.2.1]heptane-2,3-dicarboxylate isa salt of cis-endo-bicyclo[2.2.1]heptane-2,3-dicarboxylic acid.
 19. Themethod of claim 15, wherein the thermoplastic polymer compositioncontains about 100 ppm to about 3,000 ppm of the calciumbicyclo[2.2.1]heptane-2,3-dicarboxylate.
 20. The method of claim 15,wherein the thermoplastic polymer composition further comprises an acidscavenger selected from the group consisting of salts of C₁₂-C₂₂ fattyacids, hydrotalcite compounds, and mixtures thereof.
 21. The method ofclaim 20, wherein the polymer composition contains about 100 ppm toabout 3,000 ppm of the salt of the acid scavenger.